Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Leased Line High Latency Problem

I have the following routers

1 x Cisco 3600

1 x Cisco 2600

They are connected via Leased Line of 256Kbps (w/ DTU) and has been working since Y2K (current utilization is below 64Kbps), no changes in the config done.

Previously icmp between two routers is 14ms average, recently it change to over 1000ms average. I did the following;

Check Serial Interface for any error = NONE

Loopback test = OK

Telco end-to-end test = OK

Fail-over to ISDN-2 (backup) = ISDN is faster (20ms)

What could be the problem and what is the solution? One thing i notice is that the 3600 serial interface is using "weighted fair queuing" while the serial interface of 2600 is not using any, but this has been like this since day 1. I will try to change 2600 queuing to "weighted fair" tonight and see the results. Else, I will as the Telco to change the port (but this will be difficult to justify to them since their end-to-end test results are OK even though that is on the physical and data layer only)Any other suggestions are greatly appreciated.

New Member

Re: Leased Line High Latency Problem

is the response consistent at 1000ms ?

If not you may have utilisation problems.

Is the line heavily utilised ?

find out of your telco tested responce times.

how far appart (physically) are the routers ?

you might be able to debug interface packets to identify if the routers are causing the delay.

sounds like a telco issue

Re: Leased Line High Latency Problem

- The response is not consistent at 1000ms. IT ranges from 14ms up to 3000ms.

- The line is 256Kbps, the maximum utilization is 64Kbps.

- Telco test end to end for 2 hours, no error found.

- The routers are approx 30Km apart.

- Router CPU and Memory are optimum (CPU: 5% Util, MEM: 18MB free) when a problem occur.

- Already done loopback test in both routers, no problem found. Anyway "sh interface serial0/0" doesn't find any error in whatever Cisco documentation recommends.

- I suspect it's a Telco issue, because whenever there is a line problem (Serial, ATM, ISDN) Telco will test only Physical Layer which doesn't make sense because if Physical Layer is a problem, the line will not be working at all (or a lot of intermittent).

CreatePlease to create content